Ph Lower after using BBB

[Tillysaint]

I've researched this forum for my problem but I couldn't find specific answers to my problems.

I have a 22,000 Gal vinyl pool that I've had for over 15 years. I've always been a "fanatic” in regard to keeping the pool chemistry levels at the proper levels without problems.

I started using the BBB method in mid July after becoming aware of this forum & the CYA problem. I previously used the hockey pucks & baking soda from Costco. I have no problems with the BBB method at this time other than the ph is consistently falling. I’ve never had this particular consistent problem, in fact, I only had to occasionally use ph-down before the BBB method.

In mid-August, I adjusted the ph to 7.6 with soda ash that I already had when I noticed the ph dropped to 7.0. I’ve been measuring pool chemistry daily and the ph level has been steadily falling to 7.0. The TA (120 – 110) hasn’t changed much doing this period since we haven’t had any appreciable rain here in Charlotte NC where we’re in drought conditions. I have only added a small amount of water to the pool since the pool gets a lot of shade during the day.

Here are my questions:
1. What’s causing the ph to go down?
I’m using the recommended bleach - 6% Sod Hypo & 94% Inert Ingreds.

2. How do I determine the amount of 20 Mule Team Borax to use?
I used one box with no effect. I looked at the Borax calc in the Bleach Calc and it says it is not to be used for ph changes. I looked at Richard Falk’s formula spreadsheet and couldn’t figure out how to use it. If Falk’s SS is the proper tool, perhaps someone could tell me the amount of Borax I need to use & I’ll try to obtain the same value playing around with the spreadsheet.

Here are my current readings: FC=2, TC=2, TA=110, CH=160, CYA=70, TDS= 600. Never had algae or cloudy water!

Thanks for the help. Ron

[aylad]

1. What’s causing the ph to go down?
I’m using the recommended bleach - 6% Sod Hypo & 94% Inert Ingreds.

2. How do I determine the amount of 20 Mule Team Borax to use?


Ron,

What is the pH of your fill water? I would look there first, because if your fill water is low (7.0-ish), then what topping off you're doing will drive the pH down. Also, have you double-checked your testing reagents? Did you have the same problem keeping the pH up when you were using trichlor? Are you by chance using dichlor to shock? Also, is 7.0 the bottom number of the tester, or does it go lower? If 7.0 is the bottom number on your tester, then your pH may actually be a lot lower than 7.0, which is why the one box of Borax didn't appear to do any good.

If you don't adjust the pH, does it drop to 7.0 and stay there, or does it continue to fall? Some pools have their own pH at which they like to "settle", and it becomes a battle and waste of money to try to force the issue. For example, my pool "likes" to be at 7.8--unless I add acid or Borax, that's where it will stay. And even if I do add them, it only makes a temporary change--within a week it will go right back to 7.8 and stay there. I can continually add acid or borax to change it, but why bother?

In a 22K gallon pool, I would expect a box of Borax to make a significant enough change in pH for you to see it on a test, unless the pH was actually lower. I would add another box, give it an hour or so to circulate, and test again. Once you know how much Borax it took to raise it the first time, you'll get a feel for how much more to add. In my 29K gallon pool with a TA of 90, 2-3 cups of Borax usually will raise it by about 0.2.

Janet

[chem geek]

You can use The Pool Calculator (http://www.poolcalculator.com/) to estimate the amount of Borax, but it's only an estimate.

In my spreadsheet, I put in your numbers in the Initial column (assuming a pH of 7.0 and don't forget the 22,000 volume) and then put in 7.5 in the Goal column and then clicked on the "Calculate Acid/Base/TA" button with the base set to "20 Mule Team Borax (Sodium Tetraborate Decahydrate)". I then get under Borax Inputs about 199 ounces of Borax. Since there are 76 ounces to a box, that's about 2.6 boxes.

Alternatively, if I enter in 76 ounces under Borax Inputs and then click on the "Calculate pH/TA" button, I see that one box of Borax would raise the pH from 7.0 to 7.16.

However, of more concern is why your pH is dropping so much. Usually if using Trichlor the pH will drop, but when you were using Trichlor that should have been very acidic and you should have needed to use something to make the pH rise and/or TA rise so pH Up and/or Alkalinity Up (baking soda). Now that you are using bleach or chlorinating liquid, you should find the tendency for the pH to rise, not to fall, so that is very, very strange. Something very acidic is getting added to your pool -- that is the mystery.

As Janet said, test the pH of your fill water though I would doubt that it is very acidic.

Richard

[doggie]

When we used to use the pucks, it would be nothing for me to go thru 60 pounds of PH Increaser each season. Sometimes more!

Since we've gone BBB this year with fresh water (got a new liner right before closing last fall) I only added borax first thing when we opened. Ours has a settle point much like Janets and ours is 7.2. It's been right there all summer long without me having to add anything to raise the PH. Not once!

I'm really surprised your PH is still dropping. :confused:

[Tillysaint]

Many thanks for the responses.

I had my readings verified by the local Leslie's. I tested my house water & the Ph is 7.3. I really didn't add that much water and my test kit goes down to 6.8. I've own pools for over 25 years and they all have been very steady & good in regard to Ph. Last year I replaced my original liner in my current pool after 17 years due to fading & my wife was "bored" with it.

I added another box of Borax & the Ph is back up to 7.6. I'll keep you posted. I still have no clues!

Regards, Ron

[chem geek]

Ron,

Yes, keep us posted as to what happens with the pH. Also, just wanted to remind you that at a CYA level of 70 ppm that you are reporting, you want to have an absolute minimum of 5.2 ppm FC in the pool and probably want to target around 7-8 ppm FC (see Ben's Best Guess CYA chart (http://www.poolforum.com/pf2/showthread.php?t=365)). Though you may have other factors inhibiting algae in your pool, keeping to these levels of chlorine will ensure your pool does not get algae.

Richard